Method of making hollow articles



Patented Mar. 26, 1946 UNITED STATES PATENT- OFFICE METHOD OF MAKING HOLLOW ARTICLES Joseph Dahle, West Newton, Mass, assignor, by mesne assignments, to Pro-phy-lac-tic Brush Company, Northampton, Mass., a. corporation of Delaware No Drawing. Application September 30, 1942,

Serial No. 460,280

2 Claims.

hyde or tanning materials, or with a sheet of cellulose ester, such as nitrate, the surface of which can be rendered insoluble in a cellulose ester solvent by treating with a hydrolizing agent, the unreacted portion then being dissolved with a cellulose ester solvent, the invention is particularly applicable to the manufacture of hollow articles from polyvinyl alcohol, the surfaces of which can be rendered water-insoluble by. an acetalizing topochemical treatment.

In my copending applications Serial Nos. 388,143 and 388,144, filed April 11, 1941, I have described a topochemical-method of treating polyvinyl alcohol to convert the surface at least into an insoluble acetal. By this method it is possible to make water insoluble resins from polyvinyl alcohol.

When a sheet, such as a sheet of polyvinyl alcohol, is subjected to such topochemical treatment in an acetalizing bath to render the sheet water insoluble, the reaction proceeds from the exterior to the interior of the sheet. Consequently, the reaction can be stopped while the sheet has a water insoluble exterior and a Water soluble interior. The water soluble layer then can be dissolved and thus removed, leaving the two insoluble exterior layers. Since the edges of the sheet have been rendered insoluble by the treatment, they join the two insoluble layers after the intermediate layer has been dissolved out. I have found that the resulting hollow article has a substantially uniformwall thickness throughout.

If the entire sheet is subjected to the topochemical reaction, an envelope can be obtained by slitting one side and dissolving the soluble interior of the sheet. By cutting two opposing sides, a tube or cylinder can be obtained. Obviously, a great many different shapes may be produced from sheeting by this process, such as envelopes, tubes, cylinders, finger cots, mittens, gloves, covers, hot water bottles, bathingcaps, hoods, capes, balloons, annular tubes, animal shapes, etc. By starting with a hollow article, then rendering the exterior surfaces insoluble, dissolving out the solu ble interior layers, and finally separating the two exterior layers, two hollow articles may be produced which are slightly different in size and have a wall thickness slightly less than one half that of the original article.

The hollow article produced in accordance with the invention may be plasticized after its formation by immersion in a solution of a plasticizer in a solvent which is a swelling agent for the mav terial of which the hollow article is formed. Articles so produced may be given a wide range of properties varying from soft, rubbery articles of elasticity similar to rubber to less soft articles having high strengthand toughness.

The following specific examples further illustrate the practiceof the invention.

Example N0. 1

A reaction bath was made up by mixing 1800 grams paraformaldehyde with 2400 grams isoprop'anol to which 42 grams sulfuric acid had been added. The mixture was refluxed until complete solution had taken place and then filtered to remove impurities. To the clea'r solution at C. was added gradually more sulfuric acid causing a two-phase system to form. The addition of sulfuric acid was continued until the top layer of the two phases showed an acidity of about 4.0 to 5.0 grams per 100 cc., calculated as sulfuric acid. The top layer then was separated and used as the reaction bath. p

From polyvinyl alcohol sheeting, 0.005" thick, were cut out a number of pieces in the shape of a flattened finger cot and reacted for 2 minutes at 70 C. and neutralized cold, immediately. After soaking over night, it was found that water had passed through the outer insoluble layers and converted the interior soluble layer into a jelly-like mass, which liquefied on heating in boiling water. On cutting the bottoms open, the water-soluble interior was removed by washing, leaving finger cots of insolubilized polyvinyl alcohol, insoluble in hot or cold water and having, by analysis, 6.4% unreacted alcohol groups calculated as vinyl alcohol. Such objects can be plasticized with such agents as dimet-hyl or diethyl phthalate and yield soft and rubbery objects of good flexibility, strength, and elasticity.

Example No. 2

In a bath similar in composition to the one in Example 1, except that the acidity was 2.9 grams per 100 cc, calculated as sulfuric acid, were reacted at C. for periods ranging from 8 to 12 minutes, objects of different shapes cut out from polyvinyl alcohol sheeting, 0.005" thick containing 15% glycerin as plasticizer. The shapes ineluded gloves, round discs, annular sheets, water bottles and baby pants. Immediately after reaction, the objects were soaked in a neutralizing solution overnight. All the different objects had water-soluble interiors which were easily removed by opening the object at one point and dissolving the water soluble layer. The outside film was totally insoluble in water hot or cold. The objects can be plasticized with dimethyl or diethyl phthalate yielding objects of diiferent degrees of softness depending upon the amount of plasticizer taken up. They can also be dyed in suitable colors; (for instance, blue by treatment with Solantine 4GL dissolved in 'a strength of by weight in a mixture of dimethyl phthalate in alcohol and water). I

Example No. 3

Objects of diiferent shapes such as drinking cups, circular and elongated pieces for spherical and tubular balloons, inner tubes, mittens, were cut from polyvinyl sheeting having a thickness of 0.005" These pieces were placed in a bath same as above except that the acidity was 2.2 grams per 100 cc. as sulfuric acid, and were reacted at 80 C. for 2 /2 minutes, to 4 minutes. all cases, the interiors could be removed, after neutralizing the sulfuric acid by soaking overnight in'a solution of an alkaline material, such as triethanol amine or sodium hydroxide, followed by treatment in boiling water. After drying. the

' resulting hollow objects were insoluble in boiling water. They were readily plasticized by treatment with dimethyl phthalate in a swelling agent such as alcohol.

Example N 4 From a number of baths with two-phase systems made as described in Example 1, the bottom layers were removed and mixed together. The acidity of this mixture was of'the order of 22.0 to 25.0 grams per 100 cc. calculated as sulfuric acid. Objects, cut from 0.005" thick polyvinyl alcohol sheeting were reacted in the above mixture at a temperature ranging from 8 to 13C. for periods of time varying from 5 to 15 minutes followed by neutralization and soaking in water overnight. Inall cases the outer surface was insoluble and the centers water-soluble and readily removable to produce hollow objects.

I claim:

1. The method which comprises preparing a reaction bath comprising an acetalization catalyst and a substantial proportion of isopropyl-formal as the essential reactant, subjecting a sheet of polyvinyl alcohol to the action of said bath to cause the sheet to be rendered water-insoluble progressively from its outer surface inward, stopping the reaction while an intermediate watersoluble portion remains by neutralizing the catalyst in said bath, and dissolving the water soluble inner portion of said sheet.

2. The method which comprises preparing a reaction bath comprising an acetalization catalyst and a substantial proportion of isopropylformal as the essential reactant, subjecting a sheet of polyvinyl alcohol to the action of said bath to cause the sheet to be rendered water insoluble progressively from its outer surface inward, stopping the reaction while an intermediate water soluble portion remains by neutralizing the catalyst in said bath, dissolving the water soluble inner portion of said sheet, and plasticizing the resulting article by immersion in a solu- 

